A liquid transporting apparatus such as an ink-jet head, which discharges ink through its nozzles, includes a channel unit and a piezoelectric actuator. The channel unit has liquid channels formed therein. The piezoelectric actuator applies transport energy on the liquid in the channel unit. For example, FIG. 3 of Japanese Patent Application Laid-open No. 11-334087 shows an ink-jet head including a channel unit (substrate), which has a plurality of pressure chambers (pressurizing chambers) formed therein. The pressure chambers communicate with a manifold (common passage), and each of the pressure chambers communicates with a nozzle. The piezoelectric actuator is a so-called unimorph-type piezoelectric actuator, which includes a metallic vibration plate, a piezoelectric layer and upper electrodes (individual electrodes). The vibration plate is formed to cover the pressure chambers in the channel unit. The piezoelectric layer is formed on the surface of the vibration plate and made of lead zirconate titanate (PZT) or the like. The upper electrodes are formed on the surface of the piezoelectric layer, each of the upper electrodes corresponding to one of the pressure chambers.
When driving voltage is applied selectively to the upper electrodes on the piezoelectric actuator, an electric field acts through portions (driving portions) of the piezoelectric layer sandwiched between the vibration plate and the upper electrodes applied with the driving voltage. The electric field expands or contracts the driving portions in the thickness direction of the piezoelectric layer, thereby deforming the driving portions. The deformation bends areas of the vibration plate, the areas facing pressure chambers corresponding to the deformed driving portions respectively, to apply pressure to the ink in the pressure chambers.
However, in the piezoelectric actuator described in the Japanese Application Laid-open No. 11-334087, if the rigidity of the vibration plate is high at areas (in particular, areas around the driving portions) of the vibration plate which cover the pressure chambers, the deformation of the whole region of the vibration plate facing the pressure chambers is impeded. In this case, in order to apply a predetermined pressure to the ink in the pressure chambers, it is necessary to apply a high voltage to the individual electrodes, resulting in the piezoelectric actuator consuming a large amount of electric power. If the areas of the vibration plate which surround the driving portions of the piezoelectric layer are high in rigidity, there arises a phenomenon of so-called “cross talk” in which the deformation of the portion of the piezoelectric layer and vibration plate which faces one of the pressure chambers propagates to another portion of the piezoelectric layer and vibration plate which faces other pressure chamber adjacent to the pressure chamber. In this case, the driving pattern for the plurality of pressure chambers (the pattern of voltage application to the plurality of individual electrodes) causes the variation in the amount of displacement of the portions of the vibration plate which cover the pressure chambers. The variation in the amount of displacement results in the variation in the ink discharge characteristics such as droplet velocity, droplet volume and other and the like, thereby lowering the printing quality.